Scientists’ mental models of microplastics: insights into expert perceptions from an exploratory comparison of research methods

Microplastics have been studied extensively, yet considerable uncertainty remains about the risks they pose. One way to characterize the state of knowledge about a hazard and the risks it poses is to examine how scientists specializing in that hazard understand and think about it. In two complementary studies our interdisciplinary team examined how microplastics scientists understand and think about the hazards of microplastics accumulation in freshwater systems, and what risks they may pose. Each study used a different approach. Study 1 studied the causal beliefs - that is, the "mental models" - scientists applied in decision contexts. It relied on a mixture of open- and closed-ended questions, and tasks during which microplastics scientists (N = 15) were asked to think aloud. This approach revealed scientists’ causal thinking about where microplastics come from and about the health and environmental consequences of microplastics. Specifically, in Study 1 microplastics scientists emphasized household consumption as a primary source of microplastics, while acknowledging multiple direct and indirect sources and exposure pathways, and often dwelling on the uncertainties about human health consequences. Study 2 applied the M-Tool, which is a different approach to studying mental models. In Study 2 microplastics scientists (N = 38) used the M-Tool to draw causal connections between core ideas about microplastics. Top concepts selected in this exercise included waste mismanagement, textiles, plastic degradation, individual littering, and water quality. Across both studies there were commonalities in how scientists understood the sources and exposure pathways for microplastics. Scientists emphasized household consumption of plastics as a direct and indirect source of microplastics, but there were gaps in how they talked about dose–response functions. Together the two studies portray how scientists from diverse disciplines understand the potential risks of microplastics accumulation in freshwater ecosystems. Findings suggest that microplastics risk communication and management strategies can be improved by providing a broader perspective on sources of microplastics beyond household consumption, by sharing information about diverse approaches to managing risks of microplastics, and by addressing uncertainties as well as gaps between knowledge and concerns about human health effects. The novel comparative research approach explored here demonstrates the complementarities of the methods employed, which we hope will be useful for those interested in understanding the social and decision dimensions of microplastics and other environmental problems.